The purpose of cation exchange resins and condensate polishers is twofold, to remove any undesirable cations such as calcium and/or magnesium ions by ion exchange and also to act as a filter to remove particulate iron and copper oxides which are present under normal operating conditions or during outages and start-up periods. When raw water containing calcium and magnesium salts is passed through a bed of cation ion exchange resin, which is in the sodium form, the calcium and magnesium ions are replaced by sodium ions from the exchanger. Thus, the use of cation exchange resins in the sodium form results in increased sodium levels in the condensate polisher effluent during periods of hardness ingress. Low pressure boiler systems are generally unaffected by these increased sodium levels. However, high pressure boiler systems, which generally use high purity demineralized water as make-up, cannot tolerate increased sodium levels due to the production of undesirable hydroxide ions in the boiler water. These hydroxide ions can interfere with the control of coordinated phosphate programs in these high pressure boiler systems and can thus result in corrosion problems. In addition, some boiler systems are treated with volatile amine corrosion inhibitors. These volatile amines can also be exchanged for sodium in the resin which results not only in high levels of sodium, but also in the undesirable removal of the volatile amine inhibitors from the system.
When the resin bed is exhausted, (i.e. the sodium ions are depleted, as indicated by the presence of calcium or magnesium ions in the effluent), the ion exchange resin may be regenerated by passing through the resin, an aqueous solution containing an excess of salt or brine. The regeneration of cation ion exchange resins with sodium chloride has been common practice.
U.S. Pat. No. 4,753,736 discloses the use of citrate salts of volatile amines to regenerate cation-exchange condensate polishers. This reference also discloses that the use of sulphates and acetates causes precipitation problems with calcium and iron respectively.